Genomic divergence, introduction history and latitudinal adaptation of grass carp

Abstract

Understanding the genomic signatures of population differentiation is fundamental to obtain a comprehensive view of the evolutionary process of organisms. Grass carp is one of the most important fish species in the world due to its significant value in aquaculture and world-wide vegetation biocontrol. However, little is known about the contemporary population structure and also the genetic basis of adaptation to a wide range of latitudinal environments. Using 43310 SNPs generated by genotyping by sequencing in 197 grass carps from nine populations, we examined the patterns of population differentiation, historical introduction and evidence of local selection. The overall genetic differentiation across all native populations was unexpectedly low. Nevertheless, these native populations were clearly differentiated into three genetic clusters, corresponding to the Yangtze River, the Pearl River and the Heilongjiang River System, respectively. Populations in Malaysia, India and Nepal, with the earliest introduction records, most likely have an origin from the Pearl River System. Using conceptually different approaches, 451 loci were detected under potential local selection, among which 84 were annotated to have a gene feature. 19.0% of the genes under putative selection were involved in immune responses, while 42.9% of the annotated loci showed a signature of latitudinal variation. This study provides valuable information for application of genomic tools in addressing questions concerning population differentiation that was influenced by both neutral and adaptive forces, as well as human activities.